High temperature resins based on polyamides possess desirable chemical resistance, processability and heat resistance. This makes them particularly well suited for demanding high performance automotive and electrical electronics applications. There is a current and general desire in the automotive field to have high temperature resistant structures since temperatures higher than 150° C. even higher than 200° C., are often reached in under-hood areas of automobiles. When plastic parts are exposed to such high temperatures for a prolonged period, such as in automotive under-the-hood applications or in electrical/electronics applications, the mechanical properties generally tend to decrease due to the thermo-oxidation of the polymer. This phenomenon is called heat aging.
In an attempt to improve heat aging characteristics, polyhydric alcohols have been found to give significantly improved heat aging characteristics as disclosed in US patent application publication US 2010-0029819 A1 (Palmer at al). However, molded articles derived from the polyamide compositions comprising the polyhydric alcohols have a tendency to undergo surface whitening upon aging at high humidity; which is an undesirable feature for many applications.
There remains a need for thermoplastic compositions that are suitable for manufacturing articles that exhibit good mechanical properties after long-term high temperature exposure and have desirable visual properties; that is, exhibit no whitening or a low degree of whitening, upon aging at high humidity.
EP 1041109 discloses a polyamide composition comprising a polyamide resin, a polyhydric alcohol having a melting point of 150 to 280° C., that has good fluidity and mechanical strength and is useful in injection welding techniques.
US patent publication US-2012-0196962-A1 discloses a thermoplastic molding composition including an amino acid heat stabilizer having two or more carboxylic acids.
US patent publication US-2012-0196961-A1, discloses a thermoplastic molding composition including a hydroxyl amino acid heat stabilizer having one or more hydroxyl groups.
KR 20020010356 A discloses a polyamide composition comprising a polyamide resin, a plasticizer selected from the group consisting of plasticizers including lactam-based plasticizer and an epoxy resin.
U.S. Pat. No. 5,605,945 discloses a polyamide molding composition with increased viscosity, high thermal stability and favorable mechanical properties comprising a polyamide resin and a diepoxide.
U.S. Pat. No. 4,315,086 discloses a resin composition comprising a poly(phenyl oxide)/polyamide, and a member selected from the group consisting of A) liquid diene polymers, B) epoxy compounds and C) compounds having in the molecule both an ethylene carbon-carbon double bond or a carbon-carbon triple bond and a group including an carboxylic acid group.
US patent publication 2005/0228109 discloses a thermoplastic composition comprising poly(phenylene oxide), polyamide, an unsaturated carboxylic acid copolymer and/or a polymer with pendant epoxy groups.